twinglecarmen,
Hi - I'm sorry you have had experiences that made you find this site, but it's good that you DID find it - being able to 'talk' with others who have seen rages and inconsistent behavior so typical of BPD can be really helpful.
Are you feeling guilty over anything mentioned in the texts? And about needing to be NC (have No Contact) for even just a while? Sometimes it's called Taking a Break, so you can get away from the negativity, and it's not something to feel bad for needing. You can't stop your sibling for how he/she behaves, but you can decide how much of it you will be present for. A lot of times people expect you to accept poor treatment simply on the excuse of being 'family', but after all my life, 'family' is meant to be more than shared DNA or a shared home growing up. I am NC with both parents and LC with any surviving members of my family, because both of my parents are BPD, and I just cannot stop from being enmeshed and codependent when I am in contact. To save me, I have to be NC.
When I DO encounter anyone, I find myself recriminating myself over any and all contact, and even was almost guilted by a half brother (he was adopted at birth and did not meet mom until he was 35 years old, and does not have the emotional baggage with her that I do - he sees what she wants, a sad lady, alone, victimized by the world) into allowing my mother access to me via Facebook. After realizing I was pretty much panicking over the idea of her contacting me, I re-blocked her, determining I am just not in a place where contact is good for me.
Texts - if they continue, you can do a few things based on your phone type - iPhones can be set to ":)o not disturb" based on phone number. you will still get the texts, but your phone will not go off, and you can choose to read them when/if you want, or just delete the whole conversation so you won't need to get upset reading it. No one will make you read them. I don't think those with BPD realize or care how irrational their rage-texting, calling, etc. can be. They need to have their dysregulatted emotional vomit thrown somewhere - you do not have to catch it. This is like setting a boundary for yourself - give yourself permission to ignore it, to not be present for it, to not take part in it, and to not allow it to sink into your own emotions. I think that is a little of what Mike X is talking about with FOG (Fear, Obligation, Guilt) and Depersonalization.
You have a therapist who seems to be listening and giving you some sound advice.

That's really good for you in the long run. The more you learn about what you can and cannot change in the relationship wit your sibling, the less responsibility for their rages and other emotions you will feel, and the less you will need to walk on those eggshells.